Epitaxial films composed of semiconductor containing elements from group III and group V of the Periodic Table of Elements are major components in the fabrication of optoelectronic and microwave devices. These devices provide the foundation for future advances in the area of optical communication and radar technology. Consequently, a considerable research effort has evolved in an attempt to provide more useful and efficient III-V compounds of high quality. Laser, photodetectors and transistors are examples of devices used in optical communication systems and radar technology; the III-V semiconductor films --substrates are the basic structures used in the fabrication of such devices. The use of high quality III-V semiconductors of good morphology with defect-free surfaces contributes significantly to an overall improvement in the efficient operation and extended lifetime of lasers and photodetectors, thus increasing the efficiency and reliability of communication systems.
The III-V epitaxial structures and semiconductor applications, such as those employed in the fabrication of optical communication and radar systems generally include the arsenides, antimonides, phosphides and nitrides of aluminum, gallium or indium, as well as ternary and quaternary mixtures thereof. These compounds, in general, are deposited as crystalline films on semiconductor substrates by either vapor phase or liquid phase epitaxial techniques.
In vapor phase epitaxy, a number of specific processes are known for effecting the deposition of III-V films. These processes usually include the steps of reacting two gaseous mixtures within an enclosed reaction chamber to provide a III14 V compound. The two gaseous mixtures generally utilized in vapor phase epitaxy comprise as one of them, a first gaseous mixture formed by contacting a Group III element with hydrogen halide; while the other, or second gaseous mixture, is formed by mixing hydrogen, as a carrier gas, with a Group V element in gaseous form. The III-V compound resulting from the interaction of the two gaseous mixtures is then deposited as an epitaxial film onto a suitable semiconductor substrate. The semiconductor substrate may be similar or different than the material used to form the epitaxial films and generally include III-V compounds, II-VI compounds, as well as silicon and germanium.
Unfortunately, the growth of III-V ternary compounds, especially the preparation of the InGaAs, InGaP and InGaSb ternary alloys is difficult and the resulting crystalline films lack good morphological characteristics and often possess a high number of impurities. The defects produced during the growth of epitaxial films of the above type originate from a number of sources, e.g., dislocation on the substrate, inappropriate epitaxial growth conditions, and the presence of foreign matter of impurities during the growth process.
One of the better known methods for producing III-V compounds is referred to as the vapor phase epitaxial-hydride technique (VPE-Hydride). The specific details of this technique are set forth in a review paper by G. H. Olsen and T. J. Zamerowski, "Crystal Growth and Properties of Binary, Ternary and Quaternary (In, Ga) (As, P) Alloys grown by the Hydride Vapor Phase Epitaxy Technique", B.R. Pamplin (ed): Progress in Crystal Growth and Characterization, Vol. II, Pergamon Press Ltd., London (1981), pp 309-375.
In one prior technique, a double barrel quartz reactor tube was necessary to grow the III-V ternary thin films. In those reactors, each barrel contained a boat of the individual group III elements. An additional inlet was necessary for the group V hydride.
In another prior technique, the vapor phase epitaxy-hydride technique used a binary alloy such as gallium and indium, as the metallic source for that technique. The utilization of a binary alloy metal source in order to effect the growth of a ternary alloy layer promotes the formation of an epitaxial film with good morphological characteristics and fewer defects than had been achieved heretofore. The group III binary alloy metal source is placed in a quartz container or boat which in turn is placed within a single barrel quartz reactor where it reacts with hydrogen chloride flowing over the alloy to form chlorides of the group III elements, such as InCl and GaCl.
The group V source, in the form of a gaseous hydride such as arsine (AsH.sub.3), phosphine (PH.sub.3) or stibine (SbH.sub.3), then reacts with the chlorides in the mixing zone of the reactor to from III-V ternary compounds as the epitaxial films on the surfaces of a suitable semiconductor substrate, such as InP in the deposition zone of the reactor.
U.S. Pat. 4,504,329 is incorporated by reference. The preparation of lattice matched In.sub.0.53 Ga.sub.0.47 As by this technique have raised questions about the interrelationship between compositions, pressure and temperature and their effect on the quality of the lattice matched In.sub.0.53 Ga.sub.0.47 As layer.